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Java Garbage Collection Distilled

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Serial, Parallel, Concurrent, CMS, G1, Young Gen, New Gen, Old Gen, Perm Gen, Eden, Tenured, Survivor Spaces, Safepoints, and the hundreds of JVM startup flags. Does this all baffle you when trying to tune the garbage collector while trying to get the required throughput and latency from your Java application? If it does then do not worry, you are not ...

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Enhanced Groovy-based JAR/Manifest Diff Tool

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This brief blog post provides another Groovy script that provides simple differencing of two JAR (or WAR or EAR) files and their MANIFEST.MF files. It represents a combination of the JAR comparison script I blogged on earlier, Rick‘s addition of Groovy‘s CliBuilder to allow some output data to be turned off, my MANIFEST.MF comparison script, and an ability to use ...

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Spring @Bean and PropertyPlaceHolderConfigurer

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I was recently stumped by what I thought was going to be a fairly straightforward implementation – Consider the following Spring Java based bean definition file ( @Configuration):                 package root; ... @Configuration @PropertySource("classpath:root/test.props") public class SampleConfig { @Value("${test.prop}") private String attr; @Bean public SampleService sampleService() { return new SampleService(attr); } } Here ...

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Fake system clock pattern in Scala with implicit parameters

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Fake system clock is a design pattern addressing testability issues of programs heavily relying on system time. If business logic flow depends on current system time, testing various flows becomes cumbersome or even impossible. Examples of such problematic scenarios include: certain business flow runs only (or is ignored) during weekends some logic is triggered only after an hour since some ...

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MongoDB Pro Tip: Field Projections

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Did you ever learn that select * from table in RDBMS-land is bad? Of course, you did! If you’re only looking for the email address of a user and not the other 15 columns worth of data, then why ask for that data and incur a penalty? The query select email from user where user_id = 1; is far more ...

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MongoDB Geo-Spatial Mobile Demo

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Mongo: noun (pl mongo or mongos) – a monetary unit of Mongolia. Equal to one hundredth of a tugrik. Origin from Mongolian “silver” I’ve written about NoSQL DBMS [http://keyholesoftware.com/2012/10/01/is-nosql-the-sql-sequel/]. We know that there are several categories of NoSQL DBMS. MongoDB is a scalable NoSQL document-oriented data store that has built-in geo-spatial indexing. Let’s look at its characteristics and then check ...

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Java’s Reflection API

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If you have ever asked yourself questions like these: – “How do I invoke a method, having only it’s name in a String?” – “How do I list all the attributes in a class dynamically?” – “How do I write a method that resets the state of any given object to default values?” Then you have probably already heared of ...

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Android Studio with android alternative emulator:Genymotion

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Moving from Eclispe/ADT to Android Studio I was exploring some alternative configuration to improve my building environment. I came across a nice Android device emulator called Genymotion. I find it very interesting and really fast so that I decided to use it as my device emulator. In this post I will explain how to setup Android development environment using Android ...

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Java 7 try-with-resources

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Java 7 provides better resource management for resources that need to be closed when finished working with, for example files, streams, database connection and sockets. This language construct is called the try-with-resources statement. The mechanism that makes this work is called the AutoCloseable interface. The Java 7 resource classes all implement this interface. The signature of this interface looks like ...

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Why You Didn’t Get The Interview, Part II

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In August 2012 I published a blog post Why You Didn’t Get The Interview, which received a good bit of attention from readers and was republished a few times (most notably by Lifehacker).  Of course one article could not list every possible explanation that an employer or recruiter might use to discard a résumé, so I decided to revisit the ...

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